Method of molding



and has for certain Patented Oct. 23, 1928.-

UNITED STATES CLIFTON D. PETTIS, OF NEW YORK, N. Y. A

METHOD OF MOLDING.

No Drawing.

The present invention relates broadly to the art of molding, and moreparticularly to the art of forming metal castings in so-called permanentmolds, although the utility of the invention is not limited in thisrespect.

At the present time it is customary in the art to which the presentinvention relates to provide so-called permanent molds. adapted to berepeatedly used for the production of metal castings. These molds are ofsuch nature as to withstand the high temperature conditions produced bysuccessive casting operations, as distinguished from temporary molds,such for example as sand molds, which are destroyed by a single castingoperation.

This invention deals more particularly with molds of the sty-calledpermanent type,

of its objects a method of treatment of said molds in such manner as toincrease their length of life, retain their molding surfaces in morenearly their orig inal state, facilitate the removal of castings, andmaintain a lower average temperature of the molds.

. I have found that molds of the permanent type may effectively havetheir molding surfaces formed either of refractory material, such forexample as silicon carbide, or of metal, it being desirable in eithercase to so construct the molds as to facilitate heat transfer to theouter mold Walls, and then radiation of heat therefrom at a relativelyhigh rate to thereby maintain the Walls of the molding cavity at atemperature lowenough to prevent fusing of the molding surface. In thismanner, the length of life of the mold is very materially increased.Repeated experiments, however, have demonstrated the further advantagesof producing a protective coating on the molding surfaces of the mold,said coating preferably being of such nature as to preclude thepocketing of air between the coating and the mold walls. and also beingofsuch character that Application filed March 13, 1925. Serial No.15,360.

same if successful castings are to be formed. Coating a cold mold inthe'manner referred to, While possessing certain advantages, isobjectionable for the reason that it provides a large amount of volatilematter which, in contact with the hot metal, rapidly vaporizes andthereby increases the volume of gases to be vented. After each castingoperation, new oil coated chills have heretofore been applied, or theentire mold has been re-used in exactly the condition inwhich it wasleft by the previous casting operation.

In accordance with the present invention, I preferably constructa'so-called permanent mold in accordance with any established practice,either of the sectional type or of the solid type, adapted to bemanipulated as required by the particular casting to be formed therein.After the mold is set up ready for. the pouring operation, it ispreferably treated with a suitable substance, as for example, oil, asheretofore proposed, adapted under the influence of heat to lose certainof its more volatile constituents. Extensive investigations which I havemade have proven the possibility of renewing the protective coating onthe molding surfaces periodically, as for example, between successivepouring operations, Without any objection able results, and in realityWith extremely beneficial results, not only as to the finish of thecastings, but also as to preservation of the molding surfaces andincrease in the length of life thereof.

These desirable results may be accomplished by the application of asubstance, such for example as crude oil, asphalticor tar products, orthe like, while the mold is hot, whereby not only is the mold cooled. tosome extent, but the more volatile constituents of the substance areimmediately vaporized, thereby leaving a molding surface having adheringthereto not only the residue of the substance originally applied, butalso the non-"olatile portion of the substance first applied. When oilor similar material is applied to a mold While at a comparatively hightemperature, I have found that this residue is apparently of agraphitic, highly refractory nature closely adhering to the mold walls,and even resisting removal by a s raping operation.

for cooling the mold to some extent, thereby maintaining a lower averagemold temperature, which is below the fusing temperature of the mold. Inaddition to this, however, and of even greater importance, is theproduction of the protective film or coating of a nature such that it ishighly resistant to the action of a hot metal and serves to increase thelength of life of the mold by preserving the mold walls, without leavingany objectionable volatile constituents.

If desired, there may be combined with the oil a suitable amount of arefractory, heat insulating or heat resisting material, such for exampleas a powder of silica, clay, bauxite or the like.

I believe myself to be the first in the art to subject so-calledpermanent molds while in heated condition to repeated a lications of asubstance adapted to form a protective tightly adhering coating or film,substantially free from volatile ingredients and having highly heatresistant and refractory properties.

As a substitute for the substances referred to, either to be usedseparately therefrom, or in combination therewith, I may utilize amixture comprising fire clay with a suitable amount of sodium silicateand water, together with a desirable proportion of pulverized silica.This mixture may be applied locally to certain portions of the moldingsurface, as for example, directly opposite the pouring gate, as aprotective means. The mixture is adapted to be applied with the moldseither in heated condition as left by a previous casting operation, orwhen the molds are cold, as at the beginning of a pour. This mixtureforms a volatile substance within the meaning of my claims. \Vhere themixture has been applied to a cold mold, the volatile constituents maybe driven off in any desired manner. When applied to a heated moldingsurface the volatile or vaporizable constituents are immediately drivenoff, leaving a'closely adherent protective coating. Where such a mixtureis applied only locally, the hydrocarbon base oil may be subsequentlyapplied to form the completed protective coating as hereinbeforereferred to.

The advantages of the present invention arise from the method of coolingmolds by subjecting them to the cooling action of a partly volatilesubstance.

Still further advantages of the invention arise from the formation of aprotective heat resistant coating on heated molding surfaces at repeatedintervals. during the use of the mold.

I claim:

1. In the method of casting, the step consisting of applying to amolding surface a mixture of fire clay with silica, and thereafterapplying oil to said surface and said mixture.

2. In a method of casting, the step consisting of applying to a moldingsurface a mixture of fire clay with sodium silicate and silica, andthereafter spraying oil onto said surface.

3. In the method of casting, the step consisting of applying to amolding surface a mixture of fire clay with sodium silicate, water andsilica, and thereafter impregnating said mixture with a partly volatilerefractory material.

4:. In the method of forming metal castings, V

the step consisting of providing closely adherent protective layers ofdifferent natures on a molding surface while in heated condition from'aprevious casting operation and at substantially the temperature impartedby such previous casting operation.

5. In the method of forming metal castings, the steps consisting ofapplying a partly volatile substance to a molding surface while atsubstantially the temperature imparted thereto by a previous castingoperation, and thereafter applying to the molding surface a partlyvolatile substance of a different nature.

6. In the method of forming metal castings, the steps consisting ofapplying a partly volatile substance to a molding surface while atsubstantially the temperature'imparted thereto by a previous castingoperation, and thereafter applying to the molding surface animpregnating substance of a volatile nature.

7 In the method of forming metal castings, the steps consisting ofapplying a coating of fire clay and silica to a molding surface, andthereafter spraying a. partly volatile substance onto the moldingsurface and said coating while the molding surface is at substantiallythe temperature imparted thereto by a previous casting operation.

8. In the method of forming metal castings,

the steps consisting of applying a coating of fire clay and silica to amolding surface, and thereafter spraying an impregnating substance of avolatile nature onto the molding surface and said coating.

9. In the method of forming metal castings, the steps consisting ofcooling and coating a mold by spraying oil under pressure onto a moldingsurface between successive casting operations.

10. In the method of forming metal castings, the step consisting ofspraying oil under pressure onto a molding surface between successivecasting operations and while the surface is at substantially thetemperature imparted by a previous casting operation.

11. In the method of forming metal castings, the steps consisting ofproviding a closely adherent protective coating on a molding surfacewhile at substantially the temperature imparted by a previous castingoperation, renewing the coating after at least some of the successivecasting operations while the mold is at substantially said temperature,and applying to such coating a further coating having differentcharacteristics.

12. In the method of forming metal cast- I ings, the steps consistingofproviding a close- 1y adherent protective coating on a molding surfaceWhile at substantially the temperature imparted by a previous castingoperation, renewing the coating after at least some of the successivecasting operations While the mold is at substantially said temperature,and applying to such coat-ing a further coating having" differentcharacteristics and of pregnating nature.

13. In the method of forming metal castings, the steps consisting ofcooling and coating a mold by applying oil under pressure to a moldingsurface after the removal of a casting from contact therewith to effectpartial volatilization of such substance and the production of a highlyheat resistant coating on the molding surface.

l l. In the method of forming metal castings, the step consisting ofapplymg oil under an impressure to a molding surface While atsubstantially the temperature imparted thereto by a previous castingoperation to effect partial volatilization of such substance and theproduction of a highly heat resistant coating on the molding surface.

15. In the method of casting, the steps consisting of applying to amoldin surface a mixture of fire clay with silica, an thereafterapplying to said surface and mixture a volatile impregnatin substance.

16. In the method of casting, the steps consisting of a plying to amolding surface a mixture ofv re ,clay with sodium silicate and silica,and thereafter applying a volatile impregnating substance to saidsurface.

In testimony where I have hereunto set my hand. A

CLIFTON D. PETTIS.

